Cathode structure



July 27, 1948.

J. E. BEGGS CATHODE STRUCTURE Filed Feb. 12, 1944 Inventor:

James E 'Be gs, b 7V047' His Attorney.

Patented July 27, 1948 2,445,993 CATHODE STRUCTURE.

James E. Beggs, Scotia, N. Y., assignor to General Electric Company, acorporation of New York Application February 12, 1944, Serial No.522,097

12 Claims. 1

My invention relates to electron discharge devices and, in particular,to a cathode structure for such devices.

It is an object of my invention to provide a new and improved cathodestructure which may be employed with equal facility in receiving andtransmitting tubes.

In the manufacture of electron discharge devices, particularly inelectronic tubes used in radio receiving sets, one of the limitationsheretofore encountered has been the necessity of using low voltages forthe energizing of the heater employed for heating an electron emissivesurface. One factor which has discouraged the use of higher heatervoltages is that, with the rapid exhausting ordinarily given electronictubes, it is difficult to degas a cathode employing a high heatervoltage since ionization of the gas between the heater terminals occursduring the exhausting period. Another factor is the necessity ofcompletely shielding the electron stream of the tube from the magneticand electrostatic effects of the high alternating current voltage.Accordingly, it is an object of my invention to provide a new andimproved cathode structure of an electron discharge device which permitsthe use of relatively high voltages of the order of the ordinaryhousehold supply voltage for energizing the heater of such a structure.

It is another object of my invention to provide a new and improvedcathode structure for an electron discharge device which permits sealingof the device after the exhausting thereof has been completed.

Still another object of my invention is to provide an improved cathodeconstruction of an electron discharge device having a low inductance.

A still further object of my invention is to provide a new and improvedcathode structure for an electron discharge device which utilizes acompletely shielded filament to prevent the coupling of filament supplyvoltages into the electron stream.

Still another object of my invention is to provide a new and improvedcathode structure which is universal in nature and which may be employedin a wide variety of discharge tubes.

In a typical embodiment, the invention makes use of a hollow metal tubehaving an end Wall which forms a cathode for an electron dischargedevice and which encloses both a heater for the cathode and a getter forthe discharge device. The metal tube is used in cooperation with ametallic sleeve in the enclosing envelope of an elecmolten metallic sealbetween the sleeve and the metallic tube so that accurate electrodespacing may be obtained after complete evacuation of the tube. The heatsource of the tube is shielded and is substantially completely thermallyisolated from the metal tube so that the heat from the source isdirected most efficiently to the emissive cathode part.

The features of the invention desired to be protected herein are pointedout with particularity in the appended claims. The invention itself, to-

gether with further objects and advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawing in which Fig. 1 is a sectionalview of a composite cathode structure embodying the invention; Fig. 1ais an enlarged" cross section of the getter element of Fig. 1; Fig. 2 isa sectional view of an electron discharge device showing a modificationof the getter arrangement employed in the composite cathode structure;Fig. 3 is a sectional view of a cathode employing an alternative heaterstructure; and Figs. 4-6 are views, partly in section, of various typesof electron discharge tubes employing the universal cathode structuredepicted in Figs. 1-3.

Referring particularly to Fig. 1, the composite cathode structure thereillustrated includes an active or emissive part consisting of a dis [0formed of any suitable metal, for example, nickel. This disk I0 ispreferably coated on its upper surface with an activating coating, suchas a thin layer of barium and strontium carbonates, and is supported bya complex structure which includes a path of low thermal conductivitycomprising a sleeve ll formed from a thin metallic foil of a poorlyconductive material, such as an ironnickel-cobalt alloy, the lower endof sleeve I I being welded to a hollow cylindrical metallic member l2.The metallic sleeve II is provided with flanges l3 at its upper endwhich are welded between the lower surface of disk III and an eyelet l4composed of a good heat conducting material, such as nickel. Afilamentary heater is is disposed within the eyelet M in close proximityto the disk l0 and is supported by means of a first lead l6 attached toone of its ends and, in turn, rigidly aifixed to the inner surface oftube 12 and asecond lead I! attached to its other terminal.

The filamentary heater l5 suitably consists of a tubular helix oftungsten or molybdenum coated with an insulating material, such asalumina, in order to prevent short-circuiting of adjacent turns of thefilament.

tron discharge device and permits the use-of a The metal tube I2 isflanged inwardly atrits natively, heater I5 may be connected betweenleads I I and 20 with getter I9 being connected between leads I6, I'l.Leads I! and 20 pass through a vitreous seal 2| at the lower end of ytube I2, the seal 2! and disk I0 defining a substantially closed regionwithin the tubes I I and I2. Tube I2, at its lower end, may be providedwith an inwardly directed bead 22 to reenforce' the seal 2| and make ita rigid wall across the lower nor-- tion of the tube I2.

In the construction of the component parts of the cathode structure, theeyelet M is made suffi'cientl'y short that it does not extend into theconstricted portion I8 of tube 52 so that the cathod'ev k0 is relativelyfree of thermal expansion effects, the sleeve II providing a poor heatconducting pathbetween disk I I] and tube I2.

The composite cathode structure thus far describedis to be usedinconjunction with a metallic sleeve 24 which is included in theenclosing envelope of any electron discharge device employing thisparticular type of cathode structure and which. defines an aperture inthis envelope through which the cathode structure extends into thedevice. The method of manufacturing an electron discharge deviceemploying the composite cathode'structure illustrated in Fig. 1 isdisclosed and claimed in my copending application, Serial No. 501,791,filed September 10, 1943, which matured as Patent No. 2,428,618 onOctober 7, 1947, and assigned to the same assignee asthis presentapplication. Briefly, in my copending application, there is explainedthe manner in whicha tube is constructed having a metallic sleeve 2 1through which the composite cathode structure of Fig. 1 is inserted. Anelectron discharge device including the cathode structure is evacuatedin an enclosed chamber, the cathode structure being supported separatelyfrom the remaining portions of the discharge device. After suitableconditions of vacuum are established within the device, a ring of solder25, located between the sleeve 2 3 and tube I2 at the shoulder portionI8 of the latter, is melted, as by inductive heating, and allowed toform a molten sealbetween the sleeve 2d and tube. I2. Thereafter, thegetter I9 may be flashed bycurrents supplied thereto over leads I7, 29.A. small hole or aperture 26 in the metallic sleeve II providescommunication between the interior of the composite cathode structureand the region within'theremainder of the electron discharge device sothat the getter I9, after evaporation, may further reduce the gaspressure within the device to a value, for example, of the order of..01micron, creating a final vacuum condition within the device. Aperturev26 is small enoughto prevent rapid exhaustion; of the electron tube bygetter lilaso-that-if the molten seal 25 is not yet established thegetter does not compete with the vacuum pump. used. to exhaust theelectrontube.

The surface tension of the molten seal of solder 25: between thesleeve24 andtube I2 maintains the difierential pressures between. the. innerand I outersurfaces. of the'electron discharge device.

After final pressure conditions are established within the device andwhile the metallic seal is still molten, the position of the electronemissive cathode disk it with respect to the remaining electrodes of thedischarge device may be adjusted to give any desired characteristic tothe electron discharge device. Ultimately, the seal formed by the solder25 is allowed to harden, completing the manufacture of the dischargedevice.

By the use of the composite cathode structure illustrated in Fig. 1 inan electron discharge device, extremely good vacuum conditions may beobtained rapidly during production by the use of the exhaustingtechnique described so that high voltages of the order of the -120 voltordinarily available to the domestic user may be employed for energizingthe filamentary heater I5 without increasing the duration of theexhausting period and without causing ionization of gas between theterminals of heater I5. Since the heater leads I'l, Iii and the heateritself are completely enclosed within the tube 52 and sleeve Ii, allcoupling between the filament supply and the electron stream of thedischarge device is avoided.

In Fig. 2, there is shown a conventional glass or metal type ofreceiving tube employing a cathode structure of the type shown inFig. 1. The receiving tube 3!) has an enclosing envelope formed of ametal or glass portion 3! and an insulating base portion 32 whichincludes the cylindrical metallic sleeve 2 defining an aperture in theenvelope through which the composite cathode structure extends. Theelectrodes of the receiving tube 3i? are of the planar type, beingsupported from a plurality of vitreous cylinders 33. In Fig. 2 there isalso illustrated an alternative construction for the composite cathodestructure cathode Iii by heater 8% and is constructed and arranged toflash when the cathode reaches the maximum temperature required insintering the cathode so that this construction avoids the requirementof an electric current and attendant leads to flash the getter.

In Fig. 3, there is illustrated a composite cathode structure employingan alternative heater construction. The heater 35 comprises a coiled orspirally wound wire lit-of tungsten or molybdenum coated with aninsulating material 3-1; such as alumina, and is in thermal contact withthe lower surface of emissive disk Iii, being clamped between the saidlower surface and a dish-shaped element 38. Disk Iii, element 38, andflange iii of foil I I preferably are welded together to'clamp heater 35in position. One terminal 39 of the heater may be connected to thecathode structure and the other terminal of a wire it may be connectedto a source of heater current. Getter 3% may be supported from the lowersurface of element 38 and may be flashed by heating of the cathode asdescribed above in the description of the structure of Fig. 2.

In Fig. 4, there is illustrated an electric discharge device 40 forultra high frequencywapplications and which may be inserted in a concerntric type of transmission line.

constitutes the anode of the device and the composite cathode structure42 formed as illustrated in Fig. 1. The grid or control electrode 43 issupported from and connected to two metal sleeves 44 and 45 whichconcentrically surround, respectively, the lower portion of anode 4| andthe upper portion of the cathode structure 42. The cathode structure 42is surrounded by sleeve 24 which is supported from sleeve 45 through avitreous seal 46. A similar seal 41 supports anode 4| from sleeve 44.When inserted in a concentric transmission line, a tube of the type ofdischarge device 40 has its anode 4| and cathode 42 connected to theinner conductor of the transmission line and the metallic sleeves 44 and45 connected to the outer conductor. Tubes of this structure aredisclosed and claimed in my copending application, Serial No. 501,790,filed September 10, 1943, and assigned to the same assignee as thepresent invention.

In Fig. there is shown in vertical section another form of ultra highfrequency electric discharge device of the so-called light house typewhich employs the cathode construction shown in Fig. 1. In the electricdischarge device 56 shown in Fig. 5, three spaced concentric disks 5|,52, 53 are supported in mutually spaced relation by means of vitreouscylinders 54, 55. The metallic sleeve 24, which forms a part of theenclosing envelope of the device has a flanged portion 56 which isconnected to the disk 53 for alternating currents, being insulatedtherefrom for unidirectional currents by means of an insulating spacer56' and sealed thereto by means of a vitreous seal 51. Tubes of thisstructure are disclosed and claimed in my copending application, SerialNo. 436,633, filed March 28, 1942, which matured as Patent No. 2,416,565on February 25, 1947, and assigned to the same assignee as the presentinvention.

In Fig. 6 there is illustrated another form of ultra high frequency tubesuitable for use in axially aligned and adjacent space resonant cavitiesof the concentric transmission line type. The electric discharge device69 there illustrated comprises a cylindrical anode 6| and a compositecathode structure of the form illustrated in Fig. 1 and encircled by ametallic sleeve 24. A metal disk 62 supports a grid 63 in spacedrelation between the anode 6| and the electron emitting cathode. Thedisk 62 is maintained in spaced relation between the anode 6| and thecathode by means of a pair of insulating cylinders 64, 65.

In all of the illustrated embodiments of my invention, it is seen thatthe composite cathode unit may be inserted easily and precisely toobtain a desired spacing between the electron emissive surface of thecathode and a control grid or an anode. The molten metallic seal betweenthe sleeve 24 and the tube l2 provides a means whereby a very fineadjustment of such spacing may be obtained. That is, the adjustment ofspacing may be made by heating the seal to its molten condition eitherinductively or by excessive heating of the cathode. In this way tubeshaving more uniform characteristics may be manufactured. Moreover, thecathode structure, due to the use of cylinders l2 and H, has anextremely low value of inductance which permits use in tubes operatingover a very wide range of frequencies from the very low frequenciesencountered in ordinary amplifying circuits to the extremely highfrequencies used in ultra high frequency work. Since the inductance ofthe cathode structure is very low, it is apparent that tubes having verylow capacitances may be designed, thus permitting operation at very highfrequencies.

While the invention has been described by reference to a particularembodiment thereof, it will be understood that numerous modificationsmay be made by those skilled in the art without d parting from theinvention. I therefore aim in the appended claims to cover all suchequivalent variations as come within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electron discharge device having an enclosing envelope, a cathodeextending into said envelope, said cathode comprising a hollow tubehermetically sealed to said envelope, said tube having an emissive endwall lying within said envelope, a heater supported within said tube inthermal relation with said end wall, gettering material disposed withinsaid tube, means within said tube whereby said gettering material may beflashed, and means within said tube for limiting the rate of removingresidual gas from said device by said material.

2. A cathode comprising a hollow metallic structure, a metal disk sealedacross one end of said structure, said disk having an electron emissivecoating on its outer surface, insulating means sealed across saidstructure at a point spaced from said disk, said disk and saidinsulating means forming with said structure a closed chamber, a heatingelement supported Within said chamber in close proximity to said disk,and a getter material disposed within said chamber, said structurehaving a small aperture therein providing communication with saidchamber.

3. An electron discharge device having an enclosing envelope, a cathodeextending into said envelope, said cathode comprising a hollow metallicstructure hermetically sealed to said envelope, said metallic structurehaving an emissive end wall lying within said envelope, an air-tightseal across said metallic structure at a point spaced from said end walland formin therewith a substantially confined chamber, a heatersupported within said chamber in thermal relation with said end Wall,gettering material disposed within said chamber, said metallic structurehaving an aperture providing communication with the space within saidenvelope, said aperture being sufiiciently small to limit the rate ofremoving residual gas from said space by said ma terial.

4. A cathode structure comprising a metal disk having an electronemissive coating on one of its surfaces, a heating element disposed inthermal relation with the other surface of said disk, and meansconnected to said element whereby heating currents may be supplied tosaid element, and a, getter material supported in close thermalproximity to said other surface and said element whereby said getter maybe flashed by heat from said element.

5. A cathode comprising an emissive part, a hollow metallic supportingstructure therefor sealed to said part, said structure including ametallic path of low thermal conductivity adjacent said part, insulatingmeans sealed across said hollow structure at a point spaced from saidpart, said insulating means and said part defining with said structure aclosed region, a heater supported within said region in proximity tosaid part, a thermally conductive body surrounding said heater andinterposed between said heater and said path, said body having a goodthermal connec- 7 tion with said emissive part for conducting heat tosaid part and for preventing radiation of heat to said structure, andgettering means supported within said region, said metallic path havingan aperture therein providing communication with said region.

6. An electron discharge device having an enclosing envelope and acathode comprising an emissive part, a hollow metallic supportingstructure therefor sealed to said part, said structure including ametallic support of low thermal conductivity adjacent said part,insulating means sealed across said hollow structure at a point spacedfrom said part, said insulating means forming a portion of said envelopeand said insulating means and said part defining with said hollowstructure a closed region, a heater supported within said region inproximity to said part, a thermally conductive body surrounding saidheater and interposed between said heater and said support, said bodyhaving a good thermal connection with said emissive part for conductingheat to said part and for preventing radiation of heat to saidstructure, and gettering means supported within said region, saidmetallic support having an aperture therein providing communicationbetween said region and the space within said device to facilitateevacuation of said space by said gettering means.

7. An electric discharge device having an enclosing envelope, a metallicsleeve extending through an aperture in said envelope, and a cathodeextending into said envelope through said sleeve, said cathodecomprising a hollow metallic structure hermetically sealed within saidsleeve, said metallic structure having an end wall lying within saidenvelope, a vitreous seal across said metallic structure at a pointspaced from said end wall, said seal and said metallic structureconstituting a sealed closure for said aperture in said envelope, and aheater supported within said metallic structure between said end walland said seal, said end wall having an electron emissive surface heatedby said heater.

8. An electric discharge device having an enclosing envelope, a metallicsleeve extending through an aperture in said envelope, and a cathodeextending into said envelope through said sleeve, said cathodecomprising a hollow metallic structure hermetically sealed within saidsleeve, said metallic structure having an end wall lying within saidenvelope, a vitreous seal across said metallic structure at a pointspaced from said end wall, said seal and said metallicstructureconstituting a sealed closure for said aperture in saidenvelope, a heater supported within said metallic structure between saidend wall and said seal, said end wall having an electron emissivesurface heated by said heater, and a getter material disposed withinsaid metallic structure between said end wall and. said seal, saidmetallic structure having a small aperture providing communication Withthe space within said envelope.

9. A cathode structure comprising a metallic disk member, a dish-shapedmember in closely spaced relation with said disk member, said diskmember having an electron emissive coating on its surface remote fromsaid dish-shaped member, a heater disposed between said members and inthermal contact therewith, and a getter mate rial supported from saiddish-shaped member on its side opposite said heater and adapted to beflashed by heat irom said heater when said disk member is heated by saidheater for sintering purposes.

10. A cathode structure comprising a hollow metal tube, a metal disksealed across one end of said tube, said disk having an electronemissive coating on its outer surface, insulating means sealed acrosssaid tube at a point spaced from said disk, said disk and insulatingmeans forming with said tube a closed chamber, a dish-shaped metallicmember supported within said tube in closely spaced relation with saiddisk, a heating element disposed between said disk and said dishshapedelement and in thermal contact therewith, and a getter materialsupported from said dishshaped element to be flashed by said heaterelement.

11. A cathode comprising .an emissive part, a hollow metallic supportingstructure therefor sealed to said part, said structure including ametallic support of low thermal conductivity adjacent said part,insulating means sealed across said hollow structure at a point spacedfrom said part, said insulating means and said part defining with saidhollow structure a closed region, a dish shaped metallic member disposedwithin said region and in thermal contact with said part, a heaterinterposed between said part and said dishshaped member and shieldedfrom said support by said dish-shaped member, said dish-shaped memberbeing adapted to conduct heat to said part and to prevent radiation ofheat to said structure, a getter material in thermal contact with saiddish-shaped member on its side remote from said part, said metallicsupport having an aperture therein providing communicaton with saidregion.

12. A cathode comprising a hollow metallic structure, a metal disksealed across one end of said structure, said disk having an electronemissive coating on its outer surface, sealing means connected acrosssaid structure at a point spaced from said disk, a heater supportedwithin said structure between said disk and said sealing means, and agetter material disposed within said structure in close thermalproximity to the said heater and whereby said getter may be flashed byheat from said heater when said disk is heated by said heater.

' JAMES E. BEGGS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,797,990 Lucian Mar. 24, 19312,032,179 Lowry Feb. 25, 1936 2,078,892 McCullough Apr. 2'7, 19372,146,365 Batchelor Feb. 7, 1939 2,244,358 Eiwald June 3, 1941 2,341,941Mouromtseff et al. Feb. 15, 1944 2,353,743 McArthur July 18, 1944

